Compatibility fix for bitmap position off stage

[ktbee]

Resolves

Fixes some of the factors in #403 and depends on #408

Proposed Changes

Add a method for identifying skin type and if the drawable is a bitmap, always use getAABB for its bounding box when calculating its fenced position at the edge of the stage.

Reason for Changes

In Scratch 2, we used getRect to get the aabb, whose implementation seems closer to drawable.getAABB than drawable.getBounds. drawable.getAABB seems closer because Flash's getRect doesn't take into account any strokes on the shape, and drawable.getBounds uses hull points, which would take stroke into account. If the skin is a bitmap, we make sure we always use drawable.getAABB instead of drawable.getFastBounds, which might use either drawable.getBounds or drawable.getAABB.

All this being said, this fix doesn't work for SVG skins, so we're sticking with our previous tactic for getting the aabb for any non-bitmap skins.

Test Coverage

I updated sprite-goes-off-stage.sb2 to include more bitmap sprite examples to test.

[thisandagain]

/cc @kchadha

[cwillisf]

Awesome job tracking these issues down!
One quibble about implementation details, but 👍 on the general concept :)

[ktbee]

Thank you for the suggestion/feedback @cwillisf! I've implemented it in my latest round of changes, let me know what you think.

[cwillisf]

👍